Fertilizer Source Impacts on Nitrous and Nitric Oxide Emissions in Corn Cropping Systems of the Upper Midwest U.S.

It is well-established that the application of nitrogen fertilizer to soil results in emissions of nitric oxide (NO) and nitrous oxide (N₂O), which are gases that have important local, regional, and global air quality impacts.   Despite hundreds of studies reporting measurements of NO and N₂O emissions from agricultural soils, there are relatively few guidelines for managing fertilizer nitrogen to reduce these emissions while maintaining optimum levels of crop production.  We have been conducting plot-scale research for the past several years in Minnesota corn/soybean and potato cropping systems to determine if the selection of a fertilizer source or application strategy has reliable impacts on NO and N₂O emissions.  This presentation will discuss our most important findings. Our studies have shown that conventionally applied anhydrous ammonia tends to generate higher N₂O emissions, but lower NO emissions, compared with conventional, spring-applied (CU) urea in these cropping systems.  We have found some reduction in N₂O emissions using polymer-coated urea compared with CU, although not consistently. Our studies in no-till managed systems suggest that N₂O emissions can be minimized by placing fertilizers below the biologically robust surface soil layer.